Implement modules RFC

This pull request contains the implementation for the modules RFC - see xp-framework/rfc#220.

Example module
--

```php
<?php
/* This file is part of the XP framework
 *
 * $Id$
 */
  uses('rdbms.DriverManager');

  /**
   * Sybase connectivity with PHP's <tt>sybase_ct</tt> extension.
   *
   * @ext   sybase_ct
   */
  module sybase_ct {
    static function __static() {
      DriverManager::register('sybase+ct', XPClass::forName('rdbms.sybase.SybaseConnection'));
    }
  }
?>
```

Reflection
--

```php
<?php
  $module= Module::forName('sybase_ct');

  $name= $module->getName(); // 'sybase_ct'
  $apidoc= $module->getComment();

  if ($module->hasAnnotations()) {
    $annotations= $module->getAnnotations();
  }
?>
```